Periprosthetic fractures are breaks in the bone that occur around joint replacements. They usually occur after trauma, for example after a fall, or when the bone around the implant becomes weak, such as in osteoporosis. In this situation even minor forces can cause the bone to fracture. The treatment of this problem is varied but usually involves fixing the fracture with plates and screws or replacing the existing implant with a revision prosthesis which usually has a longer stem, to bypass the fracture. The last option that can be used is a megaprosthesis which is implanted after the broken pieces of bone have been removed. The soft tissue attachments of the muscle tendons are reconstructed back onto the prosthesis to maintain as much function of the limb as possible. These mega or endoprostheses have the advantage that they allow immediate weight bearing and rehabilitation.
Aseptic and septic loosening.
On occasion implants become loose, either due to infection or just because the bone has not grown onto the prosthesis. In this situation the patient may complain of pain, instability or both. The worst case scenario is that the prosthesis dislocates or bone is worn away. The resulting bone defect and infection, if present, may require specialised equipment or even custom implants to restore normal limb alignment, length and function.
If infection is present, depending on the severity and bacteria that are grown, the operation to clear the infection and reconstruct the joint may require 2 operations. The first is to clear the infection. During this surgery ALL of the infected material is removed and a temporary bone cement implant or spacer is inserted. This has antibiotics impregnated into the cement which leak out and provide local control of the infection. It's other function is to maintain the space required for the definitive implants which will come at the second surgery. Samples are taken at the first surgery to guide future antibiotic administration.
The second stage of procedure is performed once the infection in the joint is thought to be cleared. Usually this is after approximately 6 weeks of antibiotics, which are given either orally or intravenously. Blood tests are also taken to measure the amount of inflammation in the body which gives the surgeon an indication as to whether the treatment has worked and the infection is cleared. The less the inflammation the better. Once this has occurred the definitive implants can be inserted.
Revision of megaprostheses.
Mega or endoprostheses are often used in limb reconstruction, especially after tumour resection. Unfortunately endoprostheses are more prone to problems than standard orthopaedic implants. They have a larger surface area that is foreign to the body and can more easily become contaminated with bacteria which may result in a periprosthetic infection. The forces through the new limb are very different once large amounts of muscle and bone are removed and this can cause the prosthesis to loosen and rarely break.
These issues are treated in much the same way as standard implants but the process is more involved and may require the assistance of other members of the surgical team such as the plastic reconstructive surgeons.